1. Field of the Invention
The invention relates to a process for preparing nicotinic acid from solutions of ammonium nicotinate.
2. Background Art
A known process for preparing nicotinic acid is based on the oxidation of 3-methylpyridine (.beta.-picoline) with atmospheric oxygen in the presence of water with heterogeneous catalysis. However, such process has the disadvantage that, in a side reaction, some of the 3-methylpyridine is broken down in a sequence of oxidation and hydrolysis steps to form ammonia, which, together with the main product nicotinic acid, forms ammonium nicotinate. The latter, in contrast to the free nicotinic acid, is highly water soluble and thus makes the work-up of the product mixture more difficult, and furthermore it represents a loss in yield, if it cannot be converted back to nicotinic acid. The latter is possible, for example, by adding a strong acid, but this forms the ammonium salt of this acid, which must be separated off and disposed of as waste. In addition, it must be noted here that nicotinic acid, as a pyridine derivative, can also react as a base and, with an excess of the strong acids, can form a salt.